1. Field of the Invention
The present invention is directed to a measuring system and to a method for determining spectrometric measurement results with high accuracy.
2. Description of Related Art
To detect the light at the output of multichannel spectrometers, detectors which are sensitive within the entire spectral range acquired by the spectrometer are generally used according to the prior art. The multichannel detectors comprise a plurality of detector elements, also called pixels, which are arranged in arrays or matrices.
A determined partial region of the total spectral region whose light output is to be measured is associated with each pixel. Since the separation of light into its spectral components is never accomplished completely, a broadband detector of the kind mentioned above always acquires a certain proportion of light from a different spectral region not associated with the pixel in the form of false light or veiling glare, as it is called. This leads to inaccurate measurement results.
In grating spectrometers, light from diffraction orders other than veiling glare can also be acquired. Various steps to minimize the proportion of veiling glare or mutual crosstalk of spectral channels are known.
For example, U.S. Pat. No. 6,181,418 B1 describes a concentric spectrometer which has a special surface referred to as a “light trap” for reducing stray light. This light trap is integrated in the design of the imaging optics and is formed as a beveled surface. The light trap is a surface specifically designed to eliminate or mitigate stray light generated from the entrance slit. It is intended to prevent stray light, including light of different diffraction orders, from being imaged on the detector. The light trap is a beveled surface with nonreflecting, absorbent or scattering characteristics. In order to eliminate the greatest possible proportion of stray light, the beveled surface of the imaging optics is rendered coarse and additionally is coated with an optically absorbent material. In addition to this beveled surface, the inner surface of the housing of the concentric spectrometer is formed in a corresponding manner, the mechanical properties of the material such as elasticity, strength and heat resistance being crucial in the selection of material.
U.S. Pat. No. 6,700,664 B1 describes a device by means of which light beams are selectively split through linear variable filters (LVF) and transmitted to a photodetector array so as that the spectral characteristics of the transmitted light can be determined. Linear variable filters (LVF) are formed on a substrate by optical thin-film layers, and the thickness of the individual layers can vary. The LVF can be designed either as a bandpass filter or as a high/low-cut filter. The width of the selectively split light beams can be adapted to the detector so that they approximately correspond to the pixel width. It is disadvantageous in this solution that the LVF cannot be arranged on the surface of the detector array because this is difficult to accomplish owing to the sensitive surface of the detector array and the wiring of the detector array. Therefore, the different LVF elements are set on a carrier disk that is arranged at a distance of several millimeters from the detector array. Micro-objectives which focus the optical light beams on the pixels of the detector array are used to reduce the influence of unwanted light. On one hand, this makes the construction of the device more complicated; on the other hand, the micro-objectives can in turn cause additional light scattering.
In contrast to the latter, in the monolithic miniature spectrometer by Carl Zeiss Jena GmbH (Type MMS), order filters are arranged directly on the detector elements.
The problem in all of the solutions mentioned above is that it is always only possible to minimize the veiling glare, but an independent acquisition and/or compensation is not possible. Further disadvantages of the solutions mentioned above include increased resources on hardware owing to additional structural components in the spectrometer or additional optical layers on the detector.